Electronic postage meters have been developed with electronic accounting circuitry. Postage meter systems of this type are disclosed in: U.S. Pat. Nos. 3,978,457 for MICROCOMPUTERIZED ELECTRONIC POSTAGE METER SYSTEM; and in 3,938,095 for COMPUTER RESPONSIVE POSTAGE METER. The electronic accounting circuits include memory capability for storing postage accounting information. The memory function in the electronic accounting circuits have replaced the function served in postage meters by mechanical accounting registers.
Postage meters with mechanical accounting registers are not subject to many of the problems encountered by electronic postage meters. Conditions cannot normally occur in postage meters with mechanical registers that prevent accounting for a printing cycle or which result in the loss of data stored in the registers. In mechanical meters the printing mechanism is directly mechanically linked to the accounting wheels. Consequently, the printing and accounting functions are mechanically linked so that accounting occurs simultaneously with printing. Also, because of the direct linkage, the information regarding setting of the print wheels is directly coupled to the accounting registers. This is not the case in electronic postage meters where the printing is most often a mechanical function and the accounting is an electronic function. Thus, dependent reliable control of the postage printing mechanism operation including communicating setting information to the accounting circuits is critical to the proper operation of electronic postage meters. Communications is of extreme importance because of the need to reliably and accurately provide print wheel getting information to the accounting circuits so that an accurate account can be maintained of printed postage.
Postage meter printing systems suitable for use with electronic postage meters, such as disclosed in U.S. Pat. Nos. 3,965,851 for SETTING MECHANISM FOR A POSTAGE PRINTING DEVICE and 4,050,374 for METER SETTING MECHANISM, include a printing drum with a set of adjacent print wheels each of which print characters. Each print wheel is set for example to position different postage amounts for printing, by an independently rotatable gear mechanism adapted to be engaged by a master gear. The master gear is rotatably mounted within a laterally moveable carriage. The carriage can be moved to cause successive engagement with each independently rotatable gear mechanism. The printing drum is engaged to rotate to print postage by a drive gear within the meter. Other types of postage meters include bed and platen design and miniature hand held machines. In all types of postage meters it is essential that the sums recorded by the meter be the same as those printed on letters or labels.
Several methods have been used to solve the problem of locating the position of print wheels in postage meters and in other devices. The systems disclosed in U.S. Pat. Nos. 3,978,457 for MICROCOMPUTERIZED POSTAGE METER SYSTEM and 4,050,374 for METER SETTING MECHANISM employ electrooptical techniques. The system disclosed in U.S. Pat. No. 4,313,105 for ENCODING SWITCHES uses a concentric electrical contacts in conjunction with a special code. The system disclosed in U.S. Pat. No. 4,090,063 for FRANKING MACHINE COMPRISING AN ELECTRONIC COUNTERING SYSTEM uses a flexible contact brush in conjunction with a row of conductive strips. The system disclosed in U.S. Pat. No. 4,246,643 for LOW COST POSTAGE APPLICATOR employs encoder discs having patterns of conductive metals sensed with a conductive wiper.
Those of the above methods employed in systems involving postage meters achieve their intended purpose. However, the electro-optical devices require light sources which are subject to burn out. The encoders which use wipers or brushes are subject to environmental conditions including moisture and dirt. Also, these sensors can serve as sources of electromagnetic interference which can introduce unwanted signals to electronic accounting circuitry.